The heat producing core of one well known design of nuclear reactor contains multiple fuel assemblies which include a total of about 21000 fuel rods. Each fuel rod contains 240 fuel pellets used to generate heat during the reactor fission process. It therefore is apparent that more than five million pellets must be loaded into the fuel rods during the manufacturing operation. Regardless of the size of the reactor the task of loading or charging fuel rods with such a massive quantity of pellets constitutes a major factor in the reactor construction costs and in the construction time needed to fabricate a complete reactor.
According to present invention practices, the pellets are manually inserted in the fuel rods by utilizing various designs of stands and tables which support the rods in fixed predetermined positions relative to a tray containing about 25 columns of fuel pellets. Each column is accurately aligned axially with an open end of its corresponding fuel rod and an operator then manually pushes four or five columns of pellets simultaneously into the hollow rods until the pellet tray is empty. The tray is then replaced with a new supply of pellets and the process repeated about five times until each rod is full. Plugs are then welded in both ends of each rod to retain the pellets therein.
The primary disadvantage of this process is the inherent inefficiency and consequent high labor costs resulting from the effort involved in manually inserting the fuel pellets. Both the pellets and the rods are manufactured to exacting tolerances thereby requiring the pellet columns to be accurately aligned in both the X and Y planes of each rod during the loading operation. Should misalignment occur, the complete operation must be stopped until the defect is remedied. Inefficiency is particularly evident when the pellets tilt and consequently jam in the rod barrel during loading. Under this condition, the operator cannot exert sufficient force on the end of the column of pellets to break the jam and thereby free the rod for further loading. To break the jam, the rod must be lifted and vibrated manually with a mallet, or the like, to loosen the pellets from their jammed position. Upon pellet loosening, the rod must again be located in its appreciate groove and the tray then reset to continue the loading operation. Because all steps in the loading operation must be performed manually, the time to fill 20 thousand or so rods for a reactor results in direct labor costs which are disproportionately high when compared to other costs in the manufacturing cycle.